{%- set sensuserver = [] -%}

{%- for server, ipaddrs in salt['mine.get']('kroles:monitor', 'network.ip_addrs', 'grain').items() -%}
  {%- do sensuserver.append(ipaddrs){{ loop.index }} -%}
{%- endfor -%}

Below is the config file i'm using,

{
  "rabbitmq": {
    "host": "{{ sensuserver }}",
    "port": 5672,
    "vhost": "/sensu",
    "user": "sensu",
    "password": "kumo"
  }